Exopolysaccharide analysis of biofilm-forming Candida albicans

Exploring quinazoline-derived copper(I) complex coated intravaginal ring against vulvovaginal candidiasis causing Candida species

Vulvovaginal candidiasis (VVC) is especially prevalent among intrauterine device (IUD) and intravaginal ring (IVR) users. Candida albicans is the leading causative agent of VVC followed by Candida glabrata. Ascribed to the increased drug resistance by Candida spp. to the currently available drugs, this study has focused on the novel quinazoline-derived copper(I) complexes as anti-candida agents. As a novel approach, a vaginal ring was coated with the best quinazoline-derived copper(I) complex, and biofilm disruption ability was evaluated. The coated vaginal ring eradicated 70% of preformed biofilms and also inhibited the hyphal transition of Candida albicans in a simulated vaginal fluid (SVF). The overall study validates the anti-biofilm and anti-virulent properties of the metal complex-coated vaginal ring using various microscopic studies.

GC-MS Analysis of Polysaccharides from an Intergeneric Hybrid of Pleurotus florida and Cordyceps militaris: A Comparative Study

Edible and medicinal mushrooms are valuable sources of polysaccharides, known for their dual roles as immunostimulants and immunosuppressants. This study aimed to enhance polysaccharide content by fusing two mushroom species, P. florida and C. militaris, while exploring their antioxidant and antibacterial potential. These mushrooms have diverse health benefits, including lowering high cholesterol, providing anti-inflammatory effects, supporting diabetes management, aiding in cancer treatment, and enhancing the efficacy of COVID-19 vaccines. Successful hyphal fusion was achieved, and optimal culture conditions were determined using response surface methodology. The hybrids exhibited superior growth compared to the parental strains. Hyphal fusion improved several attributes, resulting in diverse hybrids with increased biomass and metabolite production. FTIR analysis confirmed the presence of exopolysaccharides, with concentrations measured at 28.4 g/L (P1), 31.50 g/L (CD), and 36.74 g/L (F3). GC-MS analysis identified various bioactive metabolites, including a higher concentration of dimethyl palmitamine in the hybrid, a novel compound, butanenitrile, 2-(methoxymethoxy), which was not found in the parental strains. These compounds are likely responsible for the enhanced antimicrobial and antioxidant activities.

Rhizoctonia solani AG1 IA extracellular polysaccharides: Structural characterization and induced resistance to rice sheath blight

Sheath blight, caused by Rhizoctonia solani (R. solani), is one of the most serious diseases of rice. Extracellular polysaccharides (EPS) are complex polysaccharides secreted by microbes that have a pivotal role in the plant-microbe interaction. At present, many studies have been carried out on R. solani, but it is not very clear whether the EPS is secreted by R. solani exists. Therefore, we isolated and extracted the EPS from R. solani, two kinds of EPS (EW-I and ES-I) were obtained by DEAE-cellulose 52 and Sephacryl S-300HR column further purification, and their structures were characterized by FT-IR, UV, GC, and NMR analysis. The results showed that EW-I and ES-I had similar monosaccharide composition but different molar ratio, they were composed of fucose, arabinose, galactose, glucose, and mannose with a ratio of 7.49: 27.72: 2.98: 6.66: 55.15 and 3.81: 12.98: 6.15: 10.83: 66.23, and their backbone may be composed of →2)-α-Manp-(1→ residues, beside ES-I was highly branched compared to EW-I. The exogenous application of EW-I and ES-I had no effect on the growth of R. solani AG1 IA itself, but their pretreatment of rice induced plant defense through activation of the salicylic acid pathway, resulting in enhanced resistance to sheath blight.

The L-Rhamnose Biosynthetic Pathway in Trichomonas vaginalis: Identification and Characterization of UDP-D-Glucose 4,6-dehydratase

Trichomonas vaginalis is the causative agent of one of the most widespread sexually transmitted diseases in the world. The adhesion of the parasite to the vaginal epithelial cells is mediated by specific proteins and by a complex glycan structure, the lipoglycan (TvLG), which covers the pathogen surface. L-rhamnose is an important component of TvLG, comprising up to 40% of the monosaccharides. Thus, the inhibition of its production could lead to a severe alteration in the TvLG structure, making the L-rhamnose biosynthetic pathway an attractive pharmacologic target. We report the identification and characterization of the first committed and limiting step of the L-rhamnose biosynthetic pathway, UDP-D-glucose 4,6-dehydratase (UGD, EC 4.2.1.76). The enzyme shows a strong preference for UDP-D-glucose compared to dTDP-D-glucose; we propose that the mechanism underlying the higher affinity for the UDP-bound substrate is mediated by the differential recognition of ribose versus the deoxyribose of the nucleotide moiety. The identification of the enzymes responsible for the following steps of the L-rhamnose pathway (epimerization and reduction) was more elusive. However, sequence analyses suggest that in T. vaginalis L-rhamnose synthesis proceeds through a mechanism different from the typical eukaryotic pathways, displaying intermediate features between the eukaryotic and prokaryotic pathways and involving separate enzymes for the epimerase and reductase activities, as observed in bacteria. Altogether, these results form the basis for a better understanding of the formation of the complex glycan structures on TvLG and the possible use of L-rhamnose biosynthetic enzymes for the development of selective inhibitors.

Streptomyces: Derived Active Extract Inhibits Candida albicans Biofilm Formation

Candida albicans is an opportunistic pathogen that causes biofilm-associated infections. C. albicans biofilms are known to display reduced susceptibility to antimicrobials and high rates of acquired antibiotic resistance, and biofilm forming in C. albicans further hampers treatment options and highlights the need for new antibiofilm strategies. Identifying active components from desert actinomycetes strains to inhibit the formation of C. albicans biofilms represents an effective treatment strategy. In this study, actinomycetes that can inhibit C. albicans biofilm formation were isolated from the Taklimakan Desert, and the underlying mechanisms were explored. After screening the anti-C.albicans biofilm activities of culture supernatants from 170 Actinomycete strains, six strains showed significant inhibition of C. albicans biofilm formation. Microscopic examination showed a reduction in biofilm formation of C. albicans treated with supernatants from actinomycetes. Scanning electron microscopy showed that the morphological changes in biofilm cells were caused by cell membrane rupture and cell material leakage. Then, C.albicans biofilms were destroyed by changing the content of extracellular polysaccharides or degrading extracellular DNA. Finally, a preliminary study on active substances extracted from a new species (TRM43335) showed that the substances that inhibited the formation of biofilms might be peptides. This study provides preliminary evidence that desert actinomyces strains have inhibitory effects on the biofilm development of C. albicans.

Characterization of Some Microorganisms from Human Stool Samples and Determination of Their Effects on CT26 Colorectal Carcinoma Cell Line

The present study aimed to isolate and identify the potential probiotic, pathobiont, and pathogenic microorganisms in the stool samples of 12 healthy individuals and evaluate their in vitro effects on cancer formation. A total of 83 strains were isolated from the stool samples and identified using MALDI-Biotyper. Fourteen of the isolates were identified as Candida spp., three isolates were identified as Cryptococcus neoformans, 55 isolates were identified as lactic acid bacteria, and the remaining isolates belonged to different 11 bacterial genera. Important microbial properties for cancer prevention and some probiotic properties were examined. All strains maintained their viability under acidic conditions and in media containing bile salts. Of the bacterial strains, 62.5% were resistant to ampicillin, chloramphenicol, gentamicin, erythromycin, kanamycin, penicillin, streptomycin, tetracycline, and vancomycin. All yeast strains were resistant to ketoconazole and susceptible to nystatin. The susceptibility of the strains to fluconazole, voriconazole, amphotericin B, and itraconazole varied. Fifty-nine percent of the strains produced EPS and 21.7% showed proteolytic activity (PA). Of the strains, 15.7% both produced exopolysaccharides (EPS) and had PA. The antioxidant activity (AOA) varied depending on the strains. The pathobiont and pathogenic microorganisms promoted tumor formation, while potential probiotic microorganisms had a suppressive effect on tumor formation (P > 0.01). One yeast (Candida kefyr MK17) and three lactic acid bacteria strains (Lacticaseibacillus paracasei MK73, Lactiplantibacillus plantarum MK55, Limosilactobacillus mucosae MK45) have superior potential thanks to their anticarcinogenic properties as well as tolerance to gastrointestinal tract conditions. Stool samples of each individual contain various potential probiotic, pathobiont, and pathogenic microorganisms.

Comparative analysis of alkaline-extracted hemicelluloses from Beech, African rose and Agba woods using FTIR and HPLC

The vast application of hemicellulose in industry is greatly influenced by its chemical components. The current study focuses on identifying the chemical components of a high yield alkaline-extracted hemicellulose and characterization to serve as a guide for more specific and effective biotechnological uses. In this study we isolated hemicellulose from sawdust of three different wood species (Beech, African rose and Agba woods) and characterized them using FTIR and HPLC techniques. Hydroxyl spectra vibrations were observed at 3919-3671 cm⁻¹ and 3454-3211 cm⁻¹ which indicates the presence of non-hydrogen bonded OH stretch and normal polymeric OH stretch in all three samples. The samples contained residual lignin indicated by IR absorption bands at 1592 and 1525 cm⁻¹. The presence of C=O stretching vibrations of acetyl groups at 1734 cm⁻¹ indicated that African rosewood was generally an acetylated molecule. Each heteropolysaccharide also contained reducing monosaccharides at their ends suggested by the C–H stretching vibrations. Infrared absorptions characteristic of asymmetric β-1,6-glycosidic stretching was present in Beechwood and Agbawood, respectively, and African rosewood gave three absorption bands β-1,3-glycosidic stretch, β-1,4-glycosidic stretch and an asymmetric β 1,6-glycosidic stretch, respectively. Agbawood gave a major absorption band at 923.75 cm⁻¹ corresponding to the absorption band at β-1,4-glycosidic stretching. African rosewood contained 96 % mannose and 4 % of an unidentified sugar. Beechwood contained primarily glucose, but Agbawood contained 20, 14, 8 and 57 % glucose, mannose, galactose, and an unidentified sugar, respectively.

An intestinal Candida albicans model for monomicrobial and polymicrobial biofilms and effects of hydrolases and the Bgl2 ligand

Background and Aim: Candida albicans is the most prevalent human fungal pathogen. In biofilms, C. albicans becomes more resistant to antifungal agents because of the production of an extracellular matrix (ECM) that protects the yeast cells. This study aimed to determine the effects of hydrolase enzymes and the Bgl2 ligand on monomicrobial and polymicrobial biofilms. Materials and Methods: Biofilm induction in rats was carried out using streptomycin (25 mg/kg) and gentamicin (7.5 mg/kg) administered orally once per day for 5 days. Rats were injected subcutaneously with cortisone acetate (225 mg/kg) as an immunosuppressant on day 5. In addition, rats were orally administered C. albicans for the single microbial model and a combination of C. albicans with Escherichia coli for the polymicrobial model. Following the biofilm production, the groups were treated with glucosamine (8.57 mg/kg body weight) and Achatina fulica hydrolases (1.5 mL) orally for 2 weeks. The reduction of the biofilm was measured using confocal laser scanning microscopy (CLSM). Data were analyzed using a t-test, with a significance value of 95%. Results: CLSM images revealed a strong association between C. albicans and E. coli in the polymicrobial biofilm. On the contrary, the combination treatment using glucosamine and A. fulica hydrolases reduced the ECM of the single microbial biofilm (53.58%). However, treatment effectiveness against the matrix (19.17%) was reduced in the polymicrobial model. Conclusion: There is a strong association between C. albicans and E. coli in the formation of polymicrobial biofilms. The combination of glucosamine and the A. fulica enzyme can reduce the single microbial biofilm ECM; however, it is ineffective in the polymicrobial model.

Compounds with Distinct Targets Present Diverse Antimicrobial and Antibiofilm Efficacy against Candida albicans and Streptococcus mutans, and Combinations of Compounds Potentiate Their Effect

Candida albicans and Streptococcus mutans interact synergistically in biofilms associated with a severe form of dental caries. Their synergism is driven by dietary sucrose. Thus, it is necessary to devise strategies to hinder the development of those biofilms and prevent cavities. Six compounds [tt-farnesol (sesquiterpene alcohol that decreases the bacterium acidogenicity and aciduricity and a quorum sensing fungal molecule), myricetin (flavonoid that interferes with S. mutans exopolysaccharides production), two 2'-hydroxychalcones and 4'-hydroxychalcone (intermediate metabolites for flavonoids), compound 1771 (inhibitor of lipoteichoic synthase in Gram-positive bacteria)] with targets in both fungus and bacterium and their products were investigated for their antimicrobial and antibiofilm activities against single-species cultures. The compounds and concentrations effective on single-species biofilms were tested alone and combined with or without fluoride to control initial and pre-formed dual-species biofilms. All the selected treatments eliminated both species on initial biofilms. In contrast, some combinations eliminated the bacterium and others the fungus in pre-formed biofilms. The combinations 4'-hydroxychalcone+tt-farnesol+myricetin, 4'-hydroxychalcone+tt-farnesol+fluoride, and all compounds together with fluoride were effective against both species in pre-formed biofilms. Therefore, combinations of compounds with distinct targets can prevent C. albicans and S. mutans dual-species biofilm build-up in vitro.

The study of the molecular mechanism of Lactobacillus paracasei clumping via divalent metal ions by electrophoretic separation

In this work, the molecular mechanism of Lactobacillus paracasei bio-colloid clumping under divalent metal ions treatment such as zinc, copper and magnesium at constant concentrations was studied. The work involved experimental (electrophoretic - capillary electrophoresis in pseudo-isotachophoresis mode, spectroscopic and spectrometric - FT-IR and MALDI-TOF-MS, microscopic - fluorescent microscopy, and flow cytometry) and theoretical (DFT calculations of model complex systems) characterization. Electrophoretic results have pointed out the formation of aggregates under the Zn²⁺ and Cu²⁺ modification, whereas the use of the Mg²⁺ allowed focusing the zone of L. paracasei biocolloid. According to the FT-IR analysis, the major functional groups involved in the aggregation are deprotonated carboxyl and amide groups derived from the bacterial surface structure. Nature of the divalent metal ions was shown to be one of the key factors influencing the bacterial aggregation process. Proteomic analysis showed that surface modification had a considerable impact on bacteria molecular profiles and protein expression, mainly linked to the activation of carbohydrate and nucleotides metabolism as well with the transcription regulation and membrane transport. Density-functional theory (DFT) calculations of modeled Cu²⁺, Mg²⁺ and Zn²⁺ coordination complexes support the interaction between the divalent metal ions and bacterial proteins. Consequently, the possible mechanism of the aggregation phenomenon was proposed. Therefore, this comprehensive study could be further applied in evaluation of biocolloid aggregation under different types of metal ions.

Development of Nano-Antifungal Therapy for Systemic and Endemic Mycoses

Fungal mycoses have become an important health and environmental concern due to the numerous deleterious side effects on the well-being of plants and humans. Antifungal therapy is limited, expensive, and unspecific (causes toxic effects), thus, more efficient alternatives need to be developed. In this work, Copper (I) Iodide (CuI) nanomaterials (NMs) were synthesized and fully characterized, aiming to develop efficient antifungal agents. The bioactivity of CuI NMs was evaluated using Sporothrix schenckii and Candida albicans as model organisms. CuI NMs were prepared as powders and as colloidal suspensions by a two-step reaction: first, the CuI2 controlled precipitation, followed by hydrazine reduction. Biopolymers (Arabic gum and chitosan) were used as surfactants to control the size of the CuI materials and to enhance its antifungal activity. The materials (powders and colloids) were characterized by SEM-EDX and AFM. The materials exhibit a hierarchical 3D shell morphology composed of ordered nanostructures. Excellent antifungal activity is shown by the NMs against pathogenic fungal strains, due to the simultaneous and multiple mechanisms of the composites to combat fungi. The minimum inhibitory concentration (MIC) and minimum fungicidal concentration (MFC) of CuI-AG and CuI-Chitosan are below 50 μg/mL (with 5 h of exposition). Optical and Atomic Force Microscopy (AFM) analyses demonstrate the capability of the materials to disrupt biofilm formation. AFM also demonstrates the ability of the materials to adhere and penetrate fungal cells, followed by their lysis and death. Following the concept of safe by design, the biocompatibility of the materials was tested. The hemolytic activity of the materials was evaluated using red blood cells. Our results indicate that the materials show an excellent antifungal activity at lower doses of hemolytic disruption.

Yeast exopolysaccharides and their physiological functions

Mounting evidence indicated the capability of various microorganisms in biosynthesis of exopolysaccharides (EPSs). A wide range of evidence extensively investigated the ability of bacterial species for EPS synthesis and their favorable effects, so little is known regarding yeast species. Many factors like composition of growth media and fermentation conditions are related to the structural and physical properties of EPSs. The EPS protects the producer yeast strain against extreme environment. Researchers proposed that yeast EPSs have priority over bacterial EPSs because of high yields of EPS biosynthesis and easy separation methods from growth media. Besides, they have drawn increasing attention due to their interesting biological activities, food, pharmaceutical, and cosmetics applications. Although a limited number of studies exist, this review aims to highlight the EPS structure and various applications of known yeast species in detail.

Classification of Clinical Isolates of Klebsiella pneumoniae Based on Their in vitro Biofilm Forming Capabilities and Elucidation of the Biofilm Matrix Chemistry With Special Reference to the Protein Content

Klebsiella pneumoniae is a human pathogen, capable of forming biofilms on abiotic and biotic surfaces. The limitations of the therapeutic options against Klebsiella pneumoniae is actually due to its innate capabilities to form biofilm and harboring determinants of multidrug resistance. We utilized a newer approach for classification of biofilm producing Klebsiella pneumoniae isolates and subsequently we evaluated the chemistry of its slime, more accurately its biofilm. We extracted and determined the amount of polysaccharides and proteins from representative bacterial biofilms. The spatial distribution of sugars and proteins were then investigated in the biofilm matrix using confocal laser scanning microscopy (CLSM). Thereafter, the extracted matrix components were subjected to sophisticated analysis incorporating Fourier transform infrared (FTIR) spectroscopy, nuclear magnetic resonance (NMR) spectroscopy, one-dimensional gel-based electrophoresis (SDS-PAGE), high performance liquid chromatography (HPLC), and MALDI MS/MS analysis. Besides, the quantification of its total proteins, total sugars, uronates, total acetyl content was also done. Results suggest sugars are not the only/major constituent of its biofilms. The proteins were harvested and subjected to SDS-PAGE which revealed various common and unique protein bands. The common band was excised and analyzed by HPLC. MALDI MS/MS results of this common protein band indicated the presence of different proteins within the biofilm. The 55 different proteins were identified including both cytosolic and membrane proteins. About 22 proteins were related to protein synthesis and processing while 15 proteins were identified related to virulence. Similarly, proteins related to energy and metabolism were 8 and those related to capsule and cell wall synthesis were 4. These results will improve our understanding of Klebsiella biofilm composition and will further help us design better strategies for controlling its biofilm such as techniques focused on weakening/targeting certain portions of the slime which is the most common building block of the biofilm matrix.

Dual-species biofilms of Streptococcus mutans and Candida albicans exhibit more biomass and are mutually beneficial compared with single-species biofilms

Background: Streptococcus mutans (Sm) and Candida albicans (Ca) are found in biofilms of early childhood caries. Objective: To characterize in vitro dual- and single-species biofilms of Sm and Ca formed on saliva-coated hydroxyapatite discs in the presence of sucrose. Design: Evaluation of biofilms included biochemical [biomass, proteins, matrix’s water-soluble (WSP) and alkali-soluble (ASP) polysaccharides, microbiological, 3D structure, gene expression, and stress tolerance analyses. Results: Biomass and proteins were higher for dual-species and lower for Ca (p = 0.001). Comparison of Sm single- and dual-species biofilms revealed no significant difference in Sm numbers or quantity of WSP (p > 0.05). Dual-species biofilms contained a higher population of Ca (p < 0.001). The quantity of ASP was higher in dual-species biofilms (vs Ca single-species biofilms; p = 0.002). The 3D structure showed larger microcolonies and distinct distribution of Sm-derived exopolysaccharides in dual-species biofilms. Compared with dual-species biofilms, expression of gtfB (ASP) and nox1 (oxidative stress) was higher for single-species of Sm whilst expression of BGL2 (matrix), PHR1 (matrix, acid tolerance) and SOD1 (oxidative stress) was higher in single-species of Ca. There was no difference for acid tolerance genes (Sm atpD and Ca PHR2), which was confirmed by acid tolerance challenge. Dual-species biofilms were more tolerant to oxidative and antimicrobial stresses (p < 0.05). Conclusions: Dual-species biofilms present greater 3D complexity, thereby, making them more resistant to stress conditions.

Biochemical alterations of Candida albicans during the phenotypic transition from yeast to hyphae captured by Fourier transform mid-infrared-attenuated reflectance spectroscopy

Candida albicans is an opportunistic human pathogen that can become virulent due to its ability to switch from a benign yeast to virulent hyphae phenotype. The emergence of C. albicans resistant to commonly used antifungal agents has necessitated the development of innovative treatments, which must be accompanied by an understanding of the molecular changes that occur during the phenotypic shift. For this purpose, Fourier transform mid-infrared spectroscopy in attenuated total reflectance mode (FT-mIR-ATR) was applied to monitor the structural and compositional changes in C. albicans during the yeast-to-hyphae transition. FT-mIR-ATR measurements were completed on the whole cell of C. albicans (SC5314) during hyphal formation induced by N-acetylglucosamine at 0, 1, 2, 3, 6 and 24 h. Principal component analysis separated the FT-mIR-ATR spectra into four groups that were aligned with the morphological changes captured by microscopic imaging. Spectral signatures indicating the structural and compositional modifications during the transition were identified mainly in the fatty acid region (3100-2800 cm-1), the protein and peptide region (1800-1500 cm-1), the mixed region (1500-1200 cm-1) and the polysaccharide region (1200-900 cm-1). A spectral fingerprint of the transition via a heat map was generated based on the peak shift in position. Quantitative evaluation of the spectra by curve fitting further revealed the dynamics of the cell's main components during the transition. This work provides valuable structural and functional information on the C. albicans phenotypic transition to hyphae, which has diagnostic implications.

Original Research Article (Experimental): Targeting fungal menace through copper nanoparticles and Tamrajal

Background

WHO reports, an escalation of antibiotic resistance in opportunistic pathogens like Candida. Tamrajal, i.e., water stored in copper vessels has been proclaimed as health elixir by ancient Ayurveda. Vis-a-Vis the use of copper contact surfaces and nanoparticles has gained significance for their antimicrobial effects. It thus seems imperative to examine copper nanoparticles and tamrajal as promising alternatives to existing antifungals.

Objective

This study not only assessed the influence of Tamrajal and copper nanoparticles on the morphological alterations of the Candida and its biofilm forming ability, but also on their ability to destroy preformed biofilms.

Materials and methods

Copper oxide nanoparticles as well as Tamrajal were evaluated as complementary as well as stand-alone antimicrobial agents. ‘Time kill assay’ and ‘germ tube inhibition test’ were performed as end-point analysis for pathogenesis, while biofilm quantification, performed to assess the colonizing capability of Candida. Scanning Electron Microscope was used for visualizing the cells, whilst ICP-AES to determine the copper concentration.

Results

92–100% cytotoxicity to the fluconazole resistant Candida species was observed with copper oxide nanoparticles as well as tamrajal during 24hr time kill assay. The study also confirmed complete germ tube inhibition by copper in both its forms in addition to the reduction in the biofilm production.

Conclusion

Compared to the classes of antifungals like azoles, echinocandins etc, copper based anti-candidal agents highlight a potential way to combat resistant candidiasis. The possibility of accumulation of NP resulting in cytotoxicity puts tamrajal as the choice due to its efficacy as well as non-toxicity as per the EPA.

Portrait of Matrix Gene Expression in Candida glabrata Biofilms with Stress Induced by Different Drugs

(1) Background: Candida glabrata is one of the most significant Candida species associated with severe cases of candidiasis. Biofilm formation is an important feature, closely associated with antifungal resistance, involving alterations of gene expression or mutations, which can result in the failure of antifungal treatments. Hence, the main goal of this work was to evaluate the role of a set of genes, associated with matrix production, in the resistance of C. glabrata biofilms to antifungal drugs. (2) Methods: the determination of the expression of BGL2, XOG1, FKS1, FKS2, GAS2, KNH1, UGP1, and MNN2 genes in 48-h biofilm’s cells of three C. glabrata strains was performed through quantitative real-time PCR (RT-qPCR), after contact with Fluconazole (Flu), Amphotericin B (AmB), Caspofungin (Csf), or Micafungin (Mcf). (3) Results: Mcf induced a general overexpression of the selected genes. It was verified that the genes related to the production of β-1,3-glucans (BGL2, XOG1, GAS2) had the highest expressions. (4) Conclusion: though β-1,6-glucans and mannans are an essential part of the cell and biofilm matrix, C. glabrata biofilm cells seem to contribute more to the replacement of β-1,3-glucans. Thus, these biopolymers seem to have a greater impact on the biofilm matrix composition and, consequently, a role in the biofilm resistance to antifungal drugs.

Liposomal and Deoxycholate Amphotericin B Formulations: Effectiveness against Biofilm Infections of Candida spp

Background: candidiasis is the primary fungal infection encountered in patients undergoing prolonged hospitalization, and the fourth leading cause of nosocomial bloodstream infections. One of the most important Candida spp. virulence factors is the ability to form biofilms, which are extremely refractory to antimicrobial therapy and very difficult to treat with the traditional antifungal therapies. It is known that the prophylaxis or treatment of a systemic candidiasis are recurrently taken without considering the possibility of a Candida spp. biofilm-related infections. Therefore, it is important to assess the effectiveness of the available drugs and which formulations have the best performance in these specific infections. Methods: 24-h-biofilms of four Candida spp. and their response to two amphotericin B (AmB) pharmaceutical formulations (liposomal and deoxycholate) were evaluated. Results: generally, Candida glabrata was the less susceptible yeast species to both AmBs. MBECs revealed that it is therapeutically more appealing to use AmB-L than AmB-Deox for all Candida spp. biofilms, since none of the determined concentrations of AmB-L reached 10% of the maximum daily dose, but both formulations showed a very good capacity in the biomass reduction. Conclusions: the liposomal formulation presents better performance in the eradication of the biofilm cells for all the species in comparison with the deoxycholate formulation.

CgMED3 Changes Membrane Sterol Composition To Help Candida glabrata Tolerate Low-pH Stress

Candida glabrata is a promising microorganism for organic acid production. The present study aimed to investigate the role of C. glabrata Mediator complex subunit 3 (CgMed3p) in protecting C. glabrata under low-pH conditions. To this end, genes CgMED3A and CgMED3B were deleted, resulting in the double-deletion Cgmed3ABΔ strain. The final biomass and cell viability levels of Cgmed3ABΔ decreased by 64.5% and 35.8%, respectively, compared to the wild-type strain results at pH 2.0. In addition, lack of CgMed3ABp resulted in selective repression of a subset of genes in the lipid biosynthesis and metabolism pathways. Furthermore, C18:1, lanosterol, zymosterol, fecosterol, and ergosterol were 13.2%, 80.4%, 40.4%, 78.1%, and 70.4% less abundant, respectively, in the Cgmed3ABΔ strain. In contrast, the concentration of squalene increased by about 44.6-fold. As a result, membrane integrity, rigidity, and H⁺-ATPase activity in the Cgmed3ABΔ strain were reduced by 62.7%, 13.0%, and 50.3%, respectively. In contrast, overexpression of CgMED3AB increased the levels of C18:0, C18:1, and ergosterol by 113.2%, 5.9%, and 26.4%, respectively. Moreover, compared to the wild-type results, dry cell weight and pyruvate production increased, irrespective of pH buffering. These results suggest that CgMED3AB regulates membrane composition, which in turn enables cells to tolerate low-pH stress. We propose that regulation of CgMed3ABp may provide a novel strategy for enhancing low-pH tolerance and increasing organic acid production by C. glabrataIMPORTANCE The objective of this study was to investigate the role of Candida glabrata Mediator complex subunit 3 (CgMed3ABp) and its regulation of gene expression at low pH in C. glabrata We found that CgMed3ABp was critical for cellular survival and pyruvate production during low-pH stress. Measures of the levels of plasma membrane fatty acids and sterol composition indicated that CgMed3ABp could play an important role in regulating homeostasis in C. glabrata We propose that controlling membrane lipid composition may enhance the robustness of C. glabrata for the production of organic acids.

Candida glabrata Biofilms: How Far Have We Come?

Infections caused by Candida species have been increasing in the last decades and can result in local or systemic infections, with high morbidity and mortality. After Candida albicans, Candida glabrata is one of the most prevalent pathogenic fungi in humans. In addition to the high antifungal drugs resistance and inability to form hyphae or secret hydrolases, C. glabrata retain many virulence factors that contribute to its extreme aggressiveness and result in a low therapeutic response and serious recurrent candidiasis, particularly biofilm formation ability. For their extraordinary organization, especially regarding the complex structure of the matrix, biofilms are very resistant to antifungal treatments. Thus, new approaches to the treatment of C. glabrata's biofilms are emerging. In this article, the knowledge available on C. glabrata's resistance will be highlighted, with a special focus on biofilms, as well as new therapeutic alternatives to control them.

Genetic alteration of UDP-rhamnose metabolism in Botrytis cinerea leads to the accumulation of UDP-KDG that adversely affects development and pathogenicity

Botrytis cinerea is a model plant-pathogenic fungus that causes grey mould and rot diseases in a wide range of agriculturally important crops. A previous study has identified two enzymes and corresponding genes (bcdh, bcer) that are involved in the biochemical transformation of uridine diphosphate (UDP)-glucose, the major fungal wall nucleotide sugar precursor, to UDP-rhamnose. We report here that deletion of bcdh, the first biosynthetic gene in the metabolic pathway, or of bcer, the second gene in the pathway, abolishes the production of rhamnose-containing glycans in these mutant strains. Deletion of bcdh or double deletion of both bcdh and bcer has no apparent effect on fungal development or pathogenicity. Interestingly, deletion of the bcer gene alone adversely affects fungal development, giving rise to altered hyphal growth and morphology, as well as reduced sporulation, sclerotia production and virulence. Treatments with wall stressors suggest the alteration of cell wall integrity. Analysis of nucleotide sugars reveals the accumulation of the UDP-rhamnose pathway intermediate UDP-4-keto-6-deoxy-glucose (UDP-KDG) in hyphae of the Δbcer strain. UDP-KDG could not be detected in hyphae of the wild-type strain, indicating fast conversion to UDP-rhamnose by the BcEr enzyme. The correlation between high UDP-KDG and modified cell wall and developmental defects raises the possibility that high levels of UDP-KDG result in deleterious effects on cell wall composition, and hence on virulence. This is the first report demonstrating that the accumulation of a minor nucleotide sugar intermediate has such a profound and adverse effect on a fungus. The ability to identify molecules that inhibit Er (also known as NRS/ER) enzymes or mimic UDP-KDG may lead to the development of new antifungal drugs.

Future therapies targeted towards eliminating Candida biofilms and associated infections

INTRODUCTION

Candida species are common human commensals and cause either superficial or invasive opportunistic infections. The biofilm form of candida as opposed to its suspended, planktonic form, is predominantly associated with these infections. Alternative or adjunctive therapies are urgently needed to manage Candida infections as the currently available short arsenal of antifungal drugs has been compromised due to their systemic toxicity, cross-reactivity with other drugs, and above all, by the emergence of drug-resistant Candida species due to irrational drug use. Areas covered: Combination anti-Candida therapies, antifungal lock therapy, denture cleansers, and mouth rinses have all been proposed as alternatives for disrupting candidal biofilms on different substrates. Other suggested approaches for the management of candidiasis include the use of natural compounds, such as probiotics, plants extracts and oils, antifungal quorum sensing molecules, anti-Candida antibodies and vaccines, cytokine therapy, transfer of primed immune cells, photodynamic therapy, and nanoparticles. Expert commentary: The sparsity of currently available antifungals and the plethora of proposed anti-candidal therapies is a distinct indication of the urgent necessity to develop efficacious therapies for candidal infections. Alternative drug delivery approaches, such as probiotics, reviewed here is likely to be a reality in clinical settings in the not too distant future.

Modulation of Candida albicans Biofilm by Different Carbon Sources

In the present investigation, the role of carbon sources (glucose, lactate, sucrose, and arabinose) on Candida albicans biofilm development and virulence factors was studied on polystyrene microtiter plates. Besides this, structural changes in cell wall component β-glucan in presence of different carbon sources have also been highlighted. Biofilm formation was analyzed by XTT (2,3-bis[2-Methoxy-4-nitro-5-sulfophenyl]-2H-tetrazolium-5-carboxanilide) reduction assay. Glucose-grown cells exhibited the highest metabolic activity during adhesion among all carbon sources tested (p < 0.05). However, cells exposed to sucrose exhibited highest biofilm formation and matrix polysaccharides secretion after 48 h. The results also correlated with the biofilm height and roughness measurements by atomic force microscopy. Exposure to lactate induced hyphal structures with the highest proteinase activity while arabinose-grown cells formed pseudohyphal structures possessing the highest phospholipase activity. Structural changes in β-glucan characterized by Fourier transform infrared (FTIR) spectroscopy displayed characteristic band of β-glucan at 892 cm(-1) in all carbon sources tested. The β(1→6) to β(1→3) glucan ratio calculated as per the band area of the peak was less in lactate (1.15) as compared to glucose (1.73), sucrose (1.62), and arabinose (2.85). These results signify that carbon sources influence C. albicans biofilm development and modulate virulence factors and structural organization of cell wall component β-glucan.

Discrimination of clinically relevant Candida species by Fourier-transform infrared spectroscopy with attenuated total reflectance (FTIR-ATR)

Accurate Candida species identification remains a challenge due to their phenotypic and genotypic similarity.

The Extracellular Matrix of Fungal Biofilms

A key feature of biofilms is their production of an extracellular matrix. This material covers the biofilm cells, providing a protective barrier to the surrounding environment. During an infection setting, this can include such offenses as host cells and products of the immune system as well as drugs used for treatment. Studies over the past two decades have revealed the matrix from different biofilm species to be as diverse as the microbes themselves. This chapter will review the composition and roles of matrix from fungal biofilms, with primary focus on Candida species, Saccharomyces cerevisiae, Aspergillus fumigatus, and Cryptococcus neoformans. Additional coverage will be provided on the antifungal resistance proffered by the Candida albicans matrix, which has been studied in the most depth. A brief section on the matrix produced by bacterial biofilms will be provided for comparison. Current tools for studying the matrix will also be discussed, as well as suggestions for areas of future study in this field.

Usnic acid inhibits biofilm formation and virulent morphological traits of Candida albicans

Biofilm formation and the yeast to hyphal switch are considered to be important virulence factors of Candida albicans. The present study reports about the potential of usnic acid, a lichen secondary metabolite inhibiting these virulent factors. Usnic acid, at its biofilm inhibitory concentration (BIC) largely reduced the viability of the metabolically active cells in matured C. albicans biofilms, exhibited significant biofilm inhibition (65%) and prevented the property of adhesion. Light microscopic images revealed that usnic acid effectively inhibited the yeast to hyphal switch and confocal microscopy showed that usnic acid greatly reduced the thickness of matured biofilms. Furthermore, usnic acid was able to reduce various sugars present in the exopolysaccharide layer (EPS) which was also confirmed by FT-IR analysis. Taken together, the present study showcases usnic acid as a potent anti-virulent compound against C. albicans and opens up a new avenue for bioprospecting lichen secondary metabolites as anti-virulent compounds.

Fungal β-1,3-glucan increases ofloxacin tolerance of Escherichia coli in a polymicrobial E. coli/Candida albicans biofilm

In the past, biofilm-related research has focused mainly on axenic biofilms. However, in nature, biofilms are often composed of multiple species, and the resulting polymicrobial interactions influence industrially and clinically relevant outcomes such as performance and drug resistance. In this study, we show that Escherichia coli does not affect Candida albicans tolerance to amphotericin or caspofungin in an E. coli/C. albicans biofilm. In contrast, ofloxacin tolerance of E. coli is significantly increased in a polymicrobial E. coli/C. albicans biofilm compared to its tolerance in an axenic E. coli biofilm. The increased ofloxacin tolerance of E. coli is mainly biofilm specific, as ofloxacin tolerance of E. coli is less pronounced in polymicrobial E. coli/C. albicans planktonic cultures. Moreover, we found that ofloxacin tolerance of E. coli decreased significantly when E. coli/C. albicans biofilms were treated with matrix-degrading enzymes such as the β-1,3-glucan-degrading enzyme lyticase. In line with a role for β-1,3-glucan in mediating ofloxacin tolerance of E. coli in a biofilm, we found that ofloxacin tolerance of E. coli increased even more in E. coli/C. albicans biofilms consisting of a high-β-1,3-glucan-producing C. albicans mutant. In addition, exogenous addition of laminarin, a polysaccharide composed mainly of poly-β-1,3-glucan, to an E. coli biofilm also resulted in increased ofloxacin tolerance. All these data indicate that β-1,3-glucan from C. albicans increases ofloxacin tolerance of E. coli in an E. coli/C. albicans biofilm.

Quantitative analysis of biofilm formation by oropharyngeal Candida albicans isolates under static conditions by confocal

Candida albicans may colonize natural or artificial surfaces, leading to formation of the biofilm. Infections associated with the biofilm formation are important therapeutic problem. In this paper, we present data concerning the biofilm formation under static conditions by oropharyngeal isolates of C. albicans on a glass surface using confocal scanning laser microscopy (CSLM). The areal parameters describing the architecture of biofilm and its development, i.e. the areal porosity, the length of edge line, the length of skeleton line, were calculated. The changes in values of these parameters during the biofilm formation by C. albicans were similar for biofilm consisting of only blastospores as well as the biofilm consisting of blastospores and filamentous elements (hyphae or/and pseudohyphae). However, the thickness of C. albicans biofilm consisting of blastospores and filamentous elements was much higher than that consisting of only blastospores. The heterogeneity may be regarded as an important feature of the yeast biofilm including C. albicans.

Candida survival strategies

Only few Candida species, e.g., Candida albicans, Candida glabrata, Candida dubliniensis, and Candida parapsilosis, are successful colonizers of a human host. Under certain circumstances these species can cause infections ranging from superficial to life-threatening disseminated candidiasis. The success of C. albicans, the most prevalent and best studied Candida species, as both commensal and human pathogen depends on its genetic, biochemical, and morphological flexibility which facilitates adaptation to a wide range of host niches. In addition, formation of biofilms provides additional protection from adverse environmental conditions. Furthermore, in many host niches Candida cells coexist with members of the human microbiome. The resulting fungal-bacterial interactions have a major influence on the success of C. albicans as commensal and also influence disease development and outcome. In this chapter, we review the current knowledge of important survival strategies of Candida spp., focusing on fundamental fitness and virulence traits of C. albicans.

Involvement of glycolysis/gluconeogenesis and signaling regulatory pathways in Saccharomyces cerevisiae biofilms during fermentation

Compared to free (free-living) cells, biofilm cells show increased resistance and stability to high-pressure fermentation conditions, although the reasons underlying these phenomena remain unclear. Here, we investigated biofilm formation with immobilized Saccharomyces cerevisiae cells grown on fiber surfaces during the process of ethanol fermentation. The development of biofilm colonies was visualized by fluorescent labeling and confocal microscopy. RNA from yeast cells at three different biofilm development periods was extracted and sequenced by high-throughput sequencing. We quantitated gene expression differences between biofilm cells and free cells and found that 2098, 1556, and 927 genes were significantly differentially expressed, respectively. We also validated the expression of previously reported genes and identified novel genes and pathways under the control of this system. Statistical analysis revealed that biofilm genes show significant gene expression changes principally in the initial period of biofilm formation compared to later periods. Carbohydrate metabolism, amino acid metabolism, signal transduction, and oxidoreductase activity were needed for biofilm formation. In contrast to previous findings, we observed some differential expression performances of FLO family genes, indicating that cell aggregation in our immobilized fermentation system was possibly independent of flocculation. Cyclic AMP-protein kinase A and mitogen-activated protein kinase pathways regulated signal transduction pathways during yeast biofilm formation. We found that carbohydrate metabolism, especially glycolysis/gluconeogenesis, played a key role in the development of S. cerevisiae biofilms. This work provides an important dataset for future studies aimed at gaining insight into the regulatory mechanisms of immobilized cells in biofilms, as well as for optimizing bioprocessing applications with S. cerevisiae.

Sustained release of a novel anti-quorum-sensing agent against oral fungal biofilms

Thiazolidinedione-8 (S-8) has recently been identified as a potential anti-quorum-sensing/antibiofilm agent against bacteria and fungi. Based on these results, we investigated the possibility of incorporating S-8 in a sustained-release membrane (SRM) to increase its pharmaceutical potential against Candida albicans biofilm. We demonstrated that SRM containing S-8 inhibits fungal biofilm formation in a time-dependent manner for 72 h, due to prolonged release of S-8. Moreover, the SRM effectively delivered the agent in its active form to locations outside the membrane reservoir. In addition, eradication of mature biofilm by the SRM containing S-8 was also significant. Of note, S-8-containing SRM affected the characteristics of mature C. albicans biofilm, such as thickness, exopolysaccharide (EPS) production, and morphogenesis of fungal cells. The concept of using an antibiofilm agent with no antifungal activity incorporated into a sustained-release delivery system is new in medicine and dentistry. This concept of an SRM containing a quorum-sensing quencher with an antibiofilm effect could pave the way for combating oral fungal infectious diseases.

A role of Candida albicans CDC4 in the negative regulation of biofilm formation

The CDC4 gene is nonessential in Candida albicans and plays a role in suppressing filamentous growth, in contrast to its homologues, which are involved in the G1-S transition of the cell cycle. While characterizing the function of C. albicans CDC4 (CaCDC4), we found that the loss of CaCDC4 resulted in a reduction in cell flocculation, indicating a possible role for CaCDC4 in biofilm formation. To elucidate the role of CaCDC4 in biofilm formation, Cacdc4 null mutant strains were constructed by using the mini-Ura-blaster method. To create a CaCDC4 rescued strain, the plasmid p6HF-ACT1p-CaCDC4 capable of constitutively expressing CaCDC4 was introduced into the Cacdc4 homozygous null mutant. To determine the biofilm formation ability, an in vitro XTT (2,3-bis-(2-methoxy-4-nitro-5-sulfophenyl)-5-[(phenylamino)carbonyl]-2H-tetrazolium-5-carboxanilide) reduction assay was used. Compared with the parental auxotrophic strain BWP17, the Cacdc4 homozygous null mutant was able to enhance biofilm formation significantly. This enhancement of biofilm formation in the Cacdc4 homozygous null mutant could be reversed by constitutively expressing CaCDC4. We conclude that CaCDC4 has a role in suppressing biofilm formation in C. albicans.

Methodologies to generate, extract, purify and fractionate yeast ECM for analytical use in proteomics and glycomics

BACKGROUND

In a multicellular organism, the extracellular matrix (ECM) provides a cell-supporting scaffold and helps maintaining the biophysical integrity of tissues and organs. At the same time it plays crucial roles in cellular communication and signalling, with implications in spatial organisation, motility and differentiation. Similarly, the presence of an ECM-like extracellular polymeric substance is known to support and protect bacterial and fungal multicellular aggregates, such as biofilms or colonies. However, the roles and composition of this microbial ECM are still poorly understood.

RESULTS

This work presents a protocol to produce S. cerevisiae and C. albicans ECM in an equally highly reproducible manner. Additionally, methodologies for the extraction and fractionation into protein and glycosidic analytical pure fractions were improved. These were subjected to analytical procedures, respectively SDS-PAGE, 2-DE, MALDI-TOF-MS and LC-MS/MS, and DAE and FPLC. Additional chemical methods were also used to test for uronic acids and sulphation.

CONCLUSIONS

The methodologies hereby presented were equally efficiently applied to extract high amounts of ECM material from S. cerevisiae and C. albicans mats, therefore showing their robustness and reproducibility for yECM molecular and structural characterization. yECM from S. cerevisiae and C. albicans displayed a different proteome and glycoside fractions. S. cerevisiae yECM presented two well-defined polysaccharides with different mass/charge, and C. albicans ECM presented a single different one. The chemical methods further suggested the presence of uronic acids, and chemical modification, possibly through sulphate substitution. All taken, the procedures herein described present the first sensible and concise approach to the molecular and chemical characterisation of the yeast ECM, opening the way to the in-depth study of the microbe multicellular aggregates structure and life-style.

Removal of Zn(II) from electroplating effluent using yeast biofilm formed on gravels: batch and column studies

BACKGROUND

Present study deals with the removal of Zn(II) ions from effluent using yeast biofilm formed on gravels.

METHODS

The biofilm forming ability of Candida rugosa and Cryptococcus laurentii was evaluated using XTT (2,3-bis[2-methoxy-4-nitro-5-sulfophenyl]-2H-tetrazolium-5-carboxanilide) reduction assay and monitored by scanning electron microscopy (SEM), and Confocal laser scanning microscopy (CLSM). Copious amount of extracellular polymeric substances (EPS) produced by yeast species was quantified and characterized by Fourier transform infrared spectroscopy (FT-IR).

RESULTS

Yeast biofilm formed on gravels by C. rugosa and C. laurentii showed 88% and 74.2% removal of Zn(II) ions respectively in batch mode. In column mode, removal of Zn(II) ions from real effluent was found to be 95.29% by C. rugosa biofilm formed on gravels.

CONCLUSION

The results of the present study showed that there is a scope to develop a cost effective method for the efficient removal of Zn(II) from effluent using gravels coated with yeast biofilm.

Antibiofilm activity of quercetin-encapsulated cytocompatible nanofibers against Candida albicans

In this study, nanofibers against pro dimorphic fungal sessile growth were developed. Quercetin was successfully encapsulated within poly(d,l-lactide- co-glycolide)–poly(ε-caprolactone) nanofibers using an electrospinning technique. Field emission scanning electron microscopy, fluorescent microscopy, and Fourier-transformed infrared spectrometer were used to confirm the formation as well as encapsulation of quercetin within the nanofibers. These fabricated nanofibers were further evaluated to determine the effectiveness of the antibiofilm activity against Candida albicans. The cytocompatibility of quercetin-encapsulated nanofibers was found to be similar to control and pure polymeric nanofibers based on 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay against human embryonic kidney (HEK-293) cell lines. These fabricated nanofibers potentially could be used as coatings on biomedical devices to inhibit microbial contaminations.

Ginger extract inhibits biofilm formation by Pseudomonas aeruginosa PA14

Bacterial biofilm formation can cause serious problems in clinical and industrial settings, which drives the development or screening of biofilm inhibitors. Some biofilm inhibitors have been screened from natural products or modified from natural compounds. Ginger has been used as a medicinal herb to treat infectious diseases for thousands of years, which leads to the hypothesis that it may contain chemicals inhibiting biofilm formation. To test this hypothesis, we evaluated ginger's ability to inhibit Pseudomonas aeruginosa PA14 biofilm formation. A static biofilm assay demonstrated that biofilm development was reduced by 39-56% when ginger extract was added to the culture. In addition, various phenotypes were altered after ginger addition of PA14. Ginger extract decreased production of extracellular polymeric substances. This finding was confirmed by chemical analysis and confocal laser scanning microscopy. Furthermore, ginger extract formed noticeably less rugose colonies on agar plates containing Congo red and facilitated swarming motility on soft agar plates. The inhibition of biofilm formation and the altered phenotypes appear to be linked to a reduced level of a second messenger, bis-(3'-5')-cyclic dimeric guanosine monophosphate. Importantly, ginger extract inhibited biofilm formation in both Gram-positive and Gram-negative bacteria. Also, surface biofilm cells formed with ginger extract detached more easily with surfactant than did those without ginger extract. Taken together, these findings provide a foundation for the possible discovery of a broad spectrum biofilm inhibitor.

Recent insights into Candida albicans biofilm resistance mechanisms

Like other microorganisms, free-living Candida albicans is mainly present in a three-dimensional multicellular structure, which is called a biofilm, rather than in a planktonic form. Candida albicans biofilms can be isolated from both abiotic and biotic surfaces at various locations within the host. As the number of abiotic implants, mainly bloodstream and urinary catheters, has been increasing, the number of biofilm-associated bloodstream or urogenital tract infections is also strongly increasing resulting in a raise in mortality. Cells within a biofilm structure show a reduced susceptibility to specific commonly used antifungals and, in addition, it has recently been shown that such cells are less sensitive to killing by components of our immune system. In this review, we summarize the most important insights in the mechanisms underlying biofilm-associated antifungal drug resistance and immune evasion strategies, focusing on the most recent advances in this area of research.

Effect of jujube honey on Candida albicans growth and biofilm formation

BACKGROUND AND AIMS

Candida species, especially Candida albicans, are major fungal pathogens of humans that are capable of causing superficial mucosal infections and systemic infections in humans. The aim of this study was to evaluate the jujube (Zizyphus spina-christi) honey for its in vitro inhibitory activity against pre-formed biofilm and its interference with the biofilm formation of C. albicans.

METHODS

The XTT reduction assay, scanning electron microscopy (SEM) and atomic force microscopy (AFM) were employed to determine the inhibitory effect of Jujube honey on C. albicans biofilm. Changes in the infrared spectrum after treatment with honey were also determined by Fourier transform infrared (FTIR) spectroscopy.

RESULTS

Jujube honey affects biofilms by decreasing the size of mature biofilms and by disruption of their structure. At a concentration of 40% w/v, it interferes with formation of C. albicans biofilms and disrupts established biofilms. The SEM and AFM results indicated that this type of honey affected the cellular morphology of C. albicans and decreased biofilm thickness.

CONCLUSIONS

The present findings show that jujube honey has antifungal properties against C. albicans and has the ability to inhibit the formation of C. albicans biofilms and disrupt established biofilms.

Methods for obtaining reliable and reproducible results in studies of Candida biofilms formed in vitro

Biofilm formation is one of the most important attributes for virulence in Candida species and contributes to increased resistance to antifungal drugs and host immune mechanisms. These features have led to the development of several methodologies to reproduce a sessile community in vitro that can be used to study the development of a biofilm, its interaction with other microorganisms and the environment, and its susceptibility to available antifungal agents and also to search for new therapy strategies. The purpose of this review is to describe the most commonly used methods to study Candida biofilms in vitro, to discuss the benefits and limitations of the different methods to induce biofilm formation, and to analyse the architecture, viability and growth kinetics of Candida biofilms.

Assessment of dentifrices against Candida biofilm

The invasion of opportunistic pleiomorphic Candida albicans into oral cavity environment leads to development and progression of its resistance to both naturally occurring antifungal peptides in human saliva as well as commercially available antifungal therapies. As a result of this, the usage and popularity of natural medicine and dentifrices had increased significantly in the last decade. In the present investigation, we have assessed the action of locally available dentifrices against C. albicans biofilm. Disk diffusion test showed maximum zone of inhibition (20 mm) by herbal dentifrice (D-5) as compared to other dentifrices when incubated at 37 °C and 48 h. Assessment of dentifrice D-5 for its effectiveness against C. albicans was further shown in MIC(90) (3.12 mg mL(-1)) and SMIC(90) (6.2 mg mL(-1)) values for planktonic and sessile cells (biofilm forming), respectively. Our data depicted 80% reduction in the cell surface hydrophobicity when 6.2 mg mL(-1) of herbal dentifrice D-5 was used against 48-h grown Candida biofilm at 37 °C. Visualization of herbal dentifrice D-5-treated C. albicans biofilm under SEM revealed drastic reduction in the dense network of yeast, hyphae, and pseudohyphae enclosed in its ECM as compared to its control biofilm. The data were further supported by CLSM analysis which depicted C. albicans architecture disruption by herbal dentifrices. From the above data, it is inferred that these studies would provide researchers and medical practitioners with better insight into the antifungal effect of natural herbal dentifrices.

Biosynthesis of UDP-4-keto-6-deoxyglucose and UDP-rhamnose in pathogenic fungi Magnaporthe grisea and Botryotinia fuckeliana

There is increasing evidence that in several fungi, rhamnose-containing glycans are involved in processes that affect host-pathogen interactions, including adhesion, recognition, virulence, and biofilm formation. Nevertheless, little is known about the pathways for the synthesis of these glycans. We show that rhamnose is present in glycans isolated from the rice pathogen Magnaporthe grisea and from the plant pathogen Botryotinia fuckeliana. We also provide evidence that these fungi produce UDP-rhamnose. This is in contrast to bacteria where dTDP-rhamnose is the activated form of this sugar. In bacteria, formation of dTDP-rhamnose requires three enzymes. Here, we demonstrate that in fungi only two genes are required for UDP-Rha synthesis. The first gene encodes a UDP-glucose-4,6-dehydratase that converts UDP-glucose to UDP-4-keto-6-deoxyglucose. The product was shown by time-resolved (1)H NMR spectroscopy to exist in solution predominantly as a hydrated form along with minor amounts of a keto form. The second gene encodes a bifunctional UDP-4-keto-6-deoxyglucose-3,5-epimerase/-4-reductase that converts UDP-4-keto-6-deoxyglucose to UDP-rhamnose. Sugar composition analysis and gene expression studies at different stages of growth indicate that the synthesis of rhamnose-containing glycans is under tissue-specific regulation. Together, our results provide new insight into the formation of rhamnose-containing glycans during the fungal life cycle. The role of these glycans in the interactions between fungal pathogens and their hosts is discussed. Knowledge of the metabolic pathways involved in the formation of rhamnose-containing glycans may facilitate the development of drugs to combat fungal diseases in humans, as to the best of our knowledge mammals do not make these types of glycans.

Biofilm formation by zygomycetes: quantification, structure and matrix composition

Most studies on fungal biofilms have focused on Candida in yeasts and Aspergillus in mycelial fungi. To the authors’ knowledge, biofilm formation by zygomycetes has not been reported previously. In this study, the biofilm-forming capacity of Rhizopus oryzae, Lichtheimia corymbifera, Rhizomucor pusillus and Apophysomyces elegans was evaluated. At appropriate seeding spore densities, Rhp . oryzae (105 c.f.u. ml−1), L. corymbifera (104 c.f.u. ml−1) and Rhm. pusillus (104 c.f.u. ml−1) produced highly intertwined, adherent structures on flat-bottomed polystyrene microtitre plates after 24 h at 37 °C. The adhered fungal hyphae were encased in an extracellular matrix, as confirmed by phase-contrast and confocal microscopy. The thickness of Rhp. oryzae, L. corymbifera and Rhm. pusillus biofilms was 109.67±10.02, 242±23.07 and 197±9.0 µm (mean±sd), respectively. Biochemical characterization of the biofilm matrix indicated the presence of glucosamine, constituting 74.54–82.22 % of its dry weight, N-acetylglucosamine, glucose and proteins. Adherence and biofilm formation were not observed in A. elegans. Although A. elegans spores germinated at all three seeding densities tested (1×107, 1×106 and 1×105 c.f.u. ml−1), no significant difference was observed (P>0.05) between the A 490 of wells inoculated with A. elegans and the cut-off A 490 for biofilm detection. This study highlights the potential for biofilm formation by at least three medically important species of zygomycetes.

Degradation of diesel oil by immobilized Candida tropicalis and biofilm formed on gravels

The performance of diesel oil degradation by Candida tropicalis immobilized on various conventional matrices (sodium alginate, carboxyl methyl cellulose, chitosan) and biowaste materials (wheat bran, sawdust, peanut hull powder) was investigated using the method of entrapment and physical adsorption. The yeast species immobilized in wheat bran showed enhanced efficiency in degrading diesel oil (98%) compared to free cells culture (80%) over a period of 7 days. Copious amount of exopolysaccharides were also produced in the presence of diesel oil. The biofilm forming ability of C. tropicalis on PVC strips was evaluated using XTT (2,3-bis[2-methoxy-4-nitro-5-sulfophenyl]-2H-tetrazolium-5-carboxanilide) reduction assay and monitored by scanning electron microscopy and atomic force microscopy. Yeast biofilm formed on gravels showed 97% degradation of diesel oil over a period of 10 days. The potential use of the biofilms for preparing trickling filters (gravel particles), for attenuating hydrocarbons in oily liquid wastes before their disposal in the open environment is suggested and discussed. This is the first successful attempt for 'artificially' establishing hydrocarbon degrading yeast biofilm on solid substrates.